Yep...same old issue....denial!
The fact of the matter is that, unfortunately, someone will list the property at or near their terms. The best way to approach this scenario is to do your homework and find the best comps available, work the numbers, and issue a realistic value range to the seller. If they are not willing to accept the opinion of a professional there is usually little that can be done to change that.....I would say that it would be best to walk away from this opportunity that resembles a realtor's "money pit."
If enough agents walk away...eventually, they should see the light....